1. Field of the Invention
The invention relates to a heat dissipating device and heat dissipating fins thereof, more particularly to a heat dissipating device having heat dissipating fins of different shapes which are stacked in a spaced-apart and alternating arrangement.
2. Description of the Related Art
Since an electronic component (such as a central processing unit or operating chip) in a computer system operates at an increased speed, the heat generated thereby also increases. In order to effectively enhance the heat dissipating efficiency of a heat dissipating device, some methods of improvement are to increase the number and area of heat dissipating fins of the heat dissipating device. However, increasing the number and area of the heat dissipating fins will not only increase the overall weight of the heat dissipating device, the flow field resistance will also rise, so that the amount of airflow supplied by a heat dissipating fan will drop when the air passes through the heat dissipating device, which will undesirably lower the heat dissipating efficiency of the heat dissipating device. Accordingly, the rotational speed of the heat dissipating fan has to be increased to overcome the problem of low airflow. However, raising the rotational speed of the fan will result in increased noise.
As shown in FIGS. 1 and 2, a conventional heat dissipating device 1 has a plurality of heat dissipating fins 11, which are generally stacked in a spaced-apart manner and which are secured on heat pipes 12 mounted on a base 10. Moreover, the heat dissipating fins 11 are of the same shape (such as a rectangular shape). During transfer of heat from the heat pipes 12 to the heat dissipating fins 11, since heat cannot be readily conducted to fin portions 111 (such as upper left and lower right corner portions shown in FIG. 2) of each fin 11 that are distal from the heat pipes 12, and since the fin portions 111 have temperatures lower than those of fin portions 112 that are proximate to the heat pipes 12, the heat conducting effect of the fin portions 111 is unsatisfactory, and the heat dissipating efficiency is poor. Furthermore, the fin portions 111 distal from the heat pipes 12 are also a source of flow field resistance, so that the amount of airflow supplied by a heat dissipating fan (not shown) will drop when the air passes through the heat dissipating fins 11 of the heat dissipating device 1 in a direction indicated by the arrows in FIG. 2, thereby lowering the heat dissipating efficiency of the heat dissipating device 1.
FIG. 3 is a comparison table listing various simulation values obtained by numerical simulation computation with respect to the amounts of the airflow which is supplied by the heat dissipating fan and which passes through the heat dissipating device 1. It is apparent from FIG. 3 that the thermal resistance values and the flow resistance values (i.e., flow field resistance) will decrease with an increase in the amounts of airflow passing through the heat dissipating device 1. The heat dissipating efficiency parameter η of the heat dissipating device 1 is defined as 1/(thermal resistance value×flow resistance value). If the thermal resistance value and the flow resistance value are small, the heat dissipating efficiency parameter η will be large, indicating that the heat dissipating efficiency of the heat dissipating device 1 is high. It can be understood from FIG. 3 that, under different environmental conditions, the heat dissipating efficiency parameter η of the heat dissipating device 1 will vary with the thermal resistance value and the flow resistance value.